Oxidation of austenitic stainless steels in PWR primary water

International audience304L and 316L SS samples are SCC-tested in PWR water for various conditions: strain level, duration, pH, surface finish. The passive Chromium-rich oxide layer, the consistent oxidation feature, is characterized using Transmission Electron Microscope analysis. EDX analysis and Energy-filtered images are used to map the oxide penetration at the surface of the sample and at contiguous grain boundaries. Statistical data obtained by these characterizations are exploited to considerate the effects of deformation, pH and duration on oxidation. Complementary analyses of intergranular crack initiations allow to invetigate the oxidation phenomenon at grain boundaries and its influence on intergranular cracking

Development of Understanding of The Interaction between Localized deformation and SCC of Austenitic Stainless Steels Exposed to Primary Environment

International audienceUnderstanding and quantification of interactions between localized deformation in materials and environmental-assisted cracking (EAC) could play an important role in maintaining the integrity of LWR components. Thus, a detailed understanding of strain localization during plastic deformation and of the underlying mechanisms is of great importance for the manufacturing and design of materials exposed to the environment of the primary circuit of PWRs. Thus, the crystal plasticity law of a 304L austenitic stainless steel has been identified, in order to quantify the effect of a change of strain path on the strain localization and increase the understanding of the contribution of the strain hardening and the strain incompatibilities on the mechanisms of initiation of SCC. Pre-deformation of the specimens used for SCC tests was evaluated using image correlation. Constant elongation rate tests and constant elongation tests were conducted for different levels of pre-deformations (0.07 < < 0.18). Examinations indicated the severe and deleterious effect of the strain localization due to a change of strain path on intergranular SCC susceptibility. Intergranular cracks initiated systematically in the low-deformed areas, where limited deformation (less than 1%) occurred during the exposure to the environment, and where high stress levels due to strain incompatibilities are expected

Corrosion sous contrainte en milieu primaire REP de l’acier inoxydable austénitique écroui 304L

This study has shown the effect of strain hardening and strain rate on the Stress Corrosion Cracking (CSC) of austenitic stainless steel AISI 304L in nominal PWR environment. A significant part of the study was focused on the conditions leading to intergranular SCC. The initiation of SCC requires that strain hardening exceeds a threshold value (310 HV0,1). Crack propagation has only been observed when a plastic strain rate was imposed at the crack-tip, in a sufficiently strain hardened material. This is related to the absence of creep in this material at 360°C. Stress corrosion cracks can follow different paths : transgranular when the material has not been pre-strained, mixed/intergranular when the material has been strained following a complex path. Observations revealed the role of the obstacles to dislocations glide on the cracking mechanims.Ce travail a mis en évidence les effets de l’écrouissage et de la vitesse de déformation plastique sur la fissuration par Corrosion Sous Contrainte (CSC) en milieu primaire nominal REP (réducteur) de l’acier inoxydable austénitique AISI 304L. Une vaste part de l’étude aconsisté à rechercher les conditions conduisant en particulier à la CSC intergranulaire. L’amorçage de la CSC nécessite le dépassement d’un seuil d’écrouissage (310 HV0,1). La propagation d’une fissure n’est observée que lorsqu’une vitesse de déformation plastique estimposée en fond de fissure, dans un matériau suffisamment écroui. Ce phénomène peut s’expliquer par l’absence de fluage à 360°C. Les fissures de CSC peuvent suivre différents chemins : transgranulaire lorsque le matériau n’a pas été pré-écroui, mixte/intergranulairelorsque le matériau est déformé suivant un trajet complexe. Les observations ont mis en évidence le rôle des obstacles au glissement des dislocations dans le matériau sur le mécanisme de CSC

Initiation of PWSCC of weld alloy 182

International audienceEven if Alloy 182 is usually exhibiting a high susceptibility to cracking in the laboratory, the field experience did not reveal to date a significant susceptibility to primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWRs), when the welds have been perfectly stress relieved. However, recently, an increasing number of cracks have been reported in the USA, Sweden and Japan on Alloy 182 and a few cases on Alloy 82. This paper addresses the work on initiation of PWSCC engaged at EDF R&D. The main objective is to calibrate an engineering model to predict the time to initiate IGSCC vs. temperature and loading for 182 weld metals having a high susceptibility to PWSCC

Oxydation intergranulaire de l'alliage 600 exposé au milieu primaire des réacteurs à eau sous pression

National audienc

Intergranular oxidation of alloy 600 exposed to simulated PWR primary water

International audienc

Amorçage de la corrosion sous contrainte (CSC) en milieu primiaire des réacteurs à eau sous pression (REP) dans les soudures en alliages base nickel 182

National audienc

Stress Concentration in the Bulk Cr2O3: Effects of Temperature and Point Defects

Modeling the growth and failure of passive oxide films formed on stainless steels is of general interest for the use of stainless steel as structural material and of special interest in the context of life time extension of light water reactors in nuclear power plants. Using the DFT+U approach, a theoretical investigation on the resistance to failure of the chromium-rich inner oxide layer formed at the surface of chromium-containing austenitic alloys (stainless steel and nickel based alloys) has been performed. The investigations were done for periodic bulk models. The data at the atomic scale were extrapolated by using the Universal Binding Energy Relationships (UBERs) model in order to estimate the mechanical behavior of a 10 μm thick oxide scale. The calculated stress values are in good agreement with experiments. Tensile stress for the bulk chromia was observed. The effects of temperature and structural defects on cracking were investigated. The possibility of cracking intensifies at high temperature compared to 0 K investigations. Higher susceptibility to cracking was observed in presence of defects compared to nondefective oxide, in agreement with experimental observation

Grain boundary oxidation of nickel base welds 182/82 in simulated PWR primary water

International audienc

Mechanical Tests in Corrosive Environments and Under Gaseous Hydrogen

International audienc